JP3805259B2 - Image processing method, image processing apparatus, and electronic camera - Google Patents

Description

【００６２】
すなわち、評価値Ｅは、各ブロックＢiごとの積算値Ｓiと重み係数Ｗiの乗算値（Ｓi×Ｗi）を全てのブロックｉ＝０〜６３について加算し、その全加算値を重み係数Ｗiの総和で除算する（加重平均を算出する）ことによって求められる。
【００６３】
次のステップ１０４では、撮像画像の明るさの平均値及び最大値を算出する。これは、撮像画像のコントラストの傾向を求めるための要素データ算出処理であり、コントラストの傾向の値（以下、コントラスト値Ｃｔという。）は、撮像画像の明るさに対する変動率に相当する。本実施の形態では、次の（２）式に示す、撮像画像に含まれる明るさの最大値と、撮像画像の明るさの平均値との比をコントラスト値に採用する。
Ｃｔ＝Ｃａｖｅ／Ｃｍａｘ ・・・（２）
但し、Ｃｍａｘは、撮像画像に含まれる明るさの最大値、Ｃａｖｅは、撮像画像の明るさの平均値を示す。
【００６４】
なお、明るさの平均値に代えて明るさの最小値や予め定めた関数により求まる平均的なレベルまたは低レベルの明るさを表す規定値でもよい。また、本実施の形態では、ブロックｉ＝０〜６３についての画像信号におけるＧ（緑）信号の積算値Ｓiを用いてコントラスト値Ｃｔを算出する。この場合、主要な画像（主要被写体の画像）が撮像画像の中央部付近に分布することが多いことなどから、撮像画像の中央部のブロックについて明るさの最大値、及び平均値を求めることが好ましい。
【００６５】
なお、ユーザの指示（図４に示す、フォーカス位置設定ボタン５１によるフォーカス位置の指示）により、フォーカス位置を変更した場合には、変更したフォーカス位置の領域を主要画像の領域として、変更したフォーカス領域のブロックについて明るさの最大値、及び平均値を求める。これにより、ユーザの指示が反映された主要被写体のコントラストを把握することができる。
【００６６】
次のステップ１０６では、上記（１）式の算出結果である評価値Ｅが「１」未満か否かを判断し、評価値Ｅが「１」未満で肯定判断のときには、ステップ１０８へ進み、評価値Ｅを「１」に置き換え、ステップ１１０へ進む。すなわち、評価値Ｅが１より小さい場合、Ｅ＝１にクリップする。一方、ステップ１０６で否定判断すなわち評価値Ｅが「１」以上で否定判断のときには、そのままステップ１１０に進む。
【００６７】
ステップ１１０では、上記のようにして算出された評価値Ｅを用いて、次の（３）式に従って画像信号の増幅度を表すゲインＧを算出する。
Ｇ＝Ｌ／Ｅ ・・・（３）
但し、Ｌは所定の目標レベルを示す値である。
【００６８】
次に、上記算出したゲインＧを、所定の上限値（ＧＵ、例えば２．０）と下限値（ＧＬ、例えば１．０）の間の値に収容（クリップ）する。まず、ステップ１１２では、算出したゲインＧに対して、下限値ＧＬ未満か否かを判断し、ゲインＧが下限値ＧＬ未満で肯定判断のときには、ステップ１１４へ進み、ゲインＧを下限値ＧＬに置き換え、ステップ１２０へ進む。すなわち、ゲインＧが下限値ＧＬより小さい場合、Ｇ＝ＧＬにクリップする。
【００６９】
一方、ステップ１１２で否定判断すなわちゲインＧが下限値ＧＬ以上で否定判断のときには、ステップ１１６に進む。ステップ１１６では、ゲインＧが上限値ＧＵを越えるか否かを判断し、ゲインＧが上限値ＧＵを越えて肯定判断のときには、ステップ１１８へ進み、ゲインＧを上限値ＧＵに置き換え、ステップ１２０へ進む。すなわち、ゲインＧが上限値ＧＵより大きい場合、Ｇ＝ＧＵにクリップする。
【００７０】
上限値にクリップするのは、ゲイン量が大きすぎると画像のＳ／Ｎが劣化するため、適度なゲイン量までで増幅を制限するものである。上限値ＧＵの具体的な設定は様々であるが、例えば、画像信号を８ビットで表す場合には、増幅率の上限を３倍までと定める。また、画像を暗くする方向に補正したくない場合には、下限値ＧＬを１に設定すればよい。
【００７１】
ステップ１２０では、抑制ゲインＣＧを算出する。抑制ゲインＣＧは、撮像画像のコントラストが大きいとき、明るさにより一義的に画像補正するゲインＧを抑制することによって、例えば背景が暗い撮影シーンであっても、被写体の明るさを適正に補正するためのものである。
【００７２】
図７に示すように、本実施の形態では、抑制ゲインＣＧは、コントラスト値Ｃｔによって定まる。すなわち、抑制ゲインＣＧとコントラスト値Ｃｔとの関係を表す特性ＣＣを予め定めておき、上記ステップ１０４で求めたコントラスト値Ｃｔに対応する抑制ゲインＣＧを算出する。特性ＣＣは、予め定めたコントラスト値Ｃｔａまで、抑制ゲインＣＧが上限値１．０を維持し、コントラスト値Ｃｔの最大値Ｃｔｂまで抑制ゲインＣＧが徐々に減少する特性である。すなわち、上記の（２）式の算出結果が大きくなるに従って、抑制ゲインＣＧは小さくなる。これは撮像画像のコントラストが小さくなるに従って抑制ゲインＣＧが小さくなるまたは、撮像画像のコントラストが大きくなるに従って抑制ゲインＣＧが大きくなることに相当する。
【００７３】
なお、抑制ゲインに上限値を設けるのは、抑制量が大きすぎると画像に対する本来のゲイン量を確保出来ない場合が想定され、適度なゲイン量まで抑制を制限するものである。
【００７４】
コントラスト値Ｃｔａは、ストロボ光が被写体まで到達していないことが想定される境界のコントラスト値Ｃｔであり、上記ステップ１１０で算出したゲインＧで補正しても、被写体の画像に影響が少ないと判別されるコントラスト値Ｃｔを実験などによって求めた平均値や統計値である。本実施の形態では、コントラスト値Ｃｔａまで抑制ゲインＣＧが１．０を維持する特性ＣＣを用いた場合を説明するが、本発明はこれに限定されるものではない。例えば、コントラスト値Ｃｔが大きくなるに従って徐々に抑制ゲインＣＧが小さくなる特性ＣＣａを採用することもできる。
【００７５】
次のステップ１２２では、上記ステップ１１０で算出したゲインＧ、及びステップ１２０で算出した抑制ゲインＣＧと、次の（４）式を用いて、最終的に画像を補正するときの補正ゲインＧａｌｌを算出する。
Ｇａｌｌ＝（Ｇ−１．０）・ＣＧ＋１．０ ・・・（４）
ステップ１２２で算出する補正ゲインＧａｌｌは、コントラスト値Ｃｔの大小によりゲインＧを抑制した補正値を求めるものである。すなわちコントラストが大きいときにはストロボ光が到達して被写体に適度の明るさの撮像画像が得られたものとして、明るさから求まるゲインＧを抑制して、主要な被写体の画像に対する画像補正量を緩和するゲインを求める。
【００７６】
なお、補正ゲインＧａｌｌを算出するための数式は、上記（４）式に限定されるものではない。例えば、ストロボ光が到達して被写体に適度の明るさの撮像画像が得られたが画像に対して、明るさから求まるゲインＧを抑制して、主要な被写体の画像に対する画像補正量を緩和するゲインを求めるものであればよく、多項式や任意の関数を用いて構成すればよい。
【００７７】
次のステップ１２４では、上記ステップ１２２で決定された補正ゲインＧａｌｌに従ってゲイン調整回路３４により画像信号を増幅し、撮像画像を補正して、本ルーチンを終了する。
【００７８】
なお、本実施の形態のステップ１００及びステップ１０２の処理は、本発明の明るさ演算手段の機能に相当し、ステップ１０４の処理は本発明のコントラスト演算手段の機能に相当する。また、ステップ１０６乃至ステップ１２２の処理は、本発明の決定手段の機能に相当し、ステップ１２４の処理が増幅手段の気のうに相当する。
【００７９】
このように、本実施の形態のカメラ１０によれば、評価値Ｅに基づいて撮影画像が光量不足である場合には、その不足の程度に応じてゲイン調整回路３４により画像信号が増幅されるので、ストロボ発光装置の発光量不足、及び発光量の制御精度の不足を補って、主要被写体が適正な明るさの画像（例えば、表示部４６に表示させたときに主要被写体たる人物の顔を見ることができるような明るさの画像）を得ることができる。
【００８０】
また、本実施の形態では、撮像画像のコントラストを算出し、そのコントラストに応じてゲイン調整回路３４で増幅する画像信号のゲインを定めている。すなわち、コントラストにより、主要な被写体にストロボ光が到達しているか否かを判別し、判別結果値（コントラスト値）から、撮影画像の明るさにより定まるゲインＧを抑制している。これによって、コントラストが大きいときにはストロボ光が到達して被写体に適度の明るさの撮像画像が得られたものとして、明るさから求まるゲインＧを抑制して、主要な被写体の画像に対する画像補正量を緩和することができ、周囲が暗い環境下で撮影した場合であっても、主要被写体が適正な明るさの画像（例えば、表示部４６に表示させたときに主要被写体などの人物の顔を見ることができるような明るさの画像）を得ることができる。
【００８１】
【発明の効果】
以上説明したように本発明によれば、撮影画像の明るさの度合い及びコントラストに基づいて増幅率を決定することで、ストロボ撮影時の被写体の撮像画像に適した増幅率を定めることができ、適正な明るさの画像を得ることができる、という効果がある。
【図面の簡単な説明】
【図１】 本発明の実施の形態に係るデジタルカメラのブロック図である。
【図２】 画像補正に利用される積算回路における撮影画面の分割形態の一例を示すイメージ図である。
【図３】 撮影画面の各ブロックに割り当てられている重み係数Ｗiの一例を示すイメージ図である。
【図４】 フォーカス位置設定ボタンの概略構成を示すイメージ図である。
【図５】 フォーカス位置設定ボタンの指示によりフォーカス領域がｈんこうされる過程を示すイメージ図である。
【図６】 本実施の形態にかかるカメラにおける画像補正の処理の流れを示すフローチャートである。
【図７】 コントラストと抑制ゲインの関係を示す特性図である。
【符号の説明】
１０…カメラ
１２…撮影光学系
１８…ＣＣＤ
２６…メモリ
３０…ＣＰＵ
３４…ゲイン調整回路
４２…メモリカード
４４…カードインターフェース
５０…操作部
５１…フォーカス位置設定ボタン
５４…ストロボ発光装置
６２…画面中心のフォーカス領域
Ｃｔ…コントラスト値
ＣＣ…特性
ＣＧ…抑制ゲイン
Ｇａｌｌ…補正ゲイン
Ｇ…ゲイン[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing method, an image processing apparatus, and an electronic camera, in particular, an image processing method and an image processing apparatus that automatically correct a captured image when an image is captured using a solid-state imaging device such as a CCD. And an electronic camera.
[0002]
[Prior art]
When shooting dark scenes with a camera device, etc., the strobe device (strobe light emitting device) needs to emit light. However, if the strobe device's light emission capability is low with respect to the distance to the subject, it emits light to the subject. The light does not reach and an image with insufficient light quantity is obtained.
[0003]
To solve this problem, obtain information on the distance to the subject, determine the amount of light emission according to this distance information, or detect the reflected light of the strobe device with the light receiving sensor (light control sensor) to obtain the appropriate amount of light. There is known a so-called auto strobe that performs control to stop the strobe emission when it reaches the maximum.
[0004]
However, highly accurate measurement accuracy and light emission control accuracy are required, and complicated control and mechanisms are required to obtain an appropriate light emission amount during photographing.
[0005]
For this reason, a technique for accurately controlling the brightness of an image by amplifying the imaged signal itself is known (see Japanese Patent Application Laid-Open No. 2001-169178). In this technology, the reachability of light to the subject during strobe light emission is determined from the weighted average value of brightness obtained using image data of the captured image during strobe light emission, and the amplification factor of the image signal is changed. .
[0006]
[Problems to be solved by the invention]
However, even when the value obtained from the image data at the time of shooting is small, the light emission from the strobe device may reach the target subject. That is, when the area on the captured image of the target subject is small, it may be determined that the captured image is dark by averaging them. In this case, the amplification factor is increased more than necessary, and image formation is not performed when the image of the target subject is displayed or recorded with appropriate brightness.
The present invention has been made in view of such circumstances, and an image processing method capable of accurately correcting an insufficient light amount of a video signal during electronic flash photography and obtaining an image with an appropriate brightness of a main subject. And an apparatus and an electronic camera equipped with the apparatus.
[0007]
In consideration of the above facts, the present invention provides an image processing method and image processing capable of obtaining a captured image of a main subject included in the captured image as an image with appropriate brightness at the time of shooting with light emission of a strobe light emitting device. The object is to obtain a device and an electronic camera.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, an image processing method of the present invention is based on an image signal obtained from an image sensor at the time of photographing accompanied by light emission of a strobe light emitting device. As a feature value of brightness including the maximum value of brightness obtained from the brightness of the entire captured image and a predetermined value set in advance Obtaining a brightness level of the captured image; obtaining a contrast of the captured image from the brightness level of the captured image; and determining a brightness level of the captured image. On the basis of the Determining the amplification factor of the image signal; When the contrast of the captured image exceeds a predetermined contrast value, Based on contrast The suppression rate for suppressing the amplification rate of the captured image is determined, and the captured image to which the determined suppression rate is added is determined. Amplifying the image signal by an amplification factor.
[0009]
In the image processing method of the present invention, first, the degree of brightness of a captured image is obtained based on an image signal obtained from an image sensor during photographing accompanied by light emission of a strobe light emitting device. The degree of brightness of the captured image refers to a characteristic value obtained from the brightness distribution of the entire captured image, and is determined by the light from the subject and the ambient light source at the time of imaging. Next, the contrast of the captured image is obtained from the brightness level of the captured image. The contrast here refers to the light / dark ratio of the captured image, and the contrast increases as the difference or ratio of the brightness between the bright part and the dark part increases. For example, when a single person is photographed in the dark with strobe light emission, if the strobe light reaches the person, the person who is the subject becomes brighter and the others become darker, so the contrast increases.
[0010]
Next, the amplification factor of the image signal is determined based on the brightness level and contrast obtained from the captured image, and the image signal is amplified by the determined amplification factor. The amplification factor is determined so that the image of the subject included in the captured image is provided with optimum brightness. That is, even when the brightness level is small, when the contrast is high, the captured image often includes an image of a subject that is appropriately illuminated by strobe light emission. Therefore, when the degree of brightness is small and the contrast is large, the amplification factor is determined based on the region where the degree of brightness included in the captured image is large, so that an amplification factor suitable for the captured image of the subject during flash photography can be obtained. Can be determined, and an image with appropriate brightness can be obtained.
[0011]
In the present invention, For the contrast of the captured image, a ratio between the maximum brightness value and a predetermined value (minimum value or average value) is used as the brightness level of the captured image. Can The
[0012]
As described above, the brightness level of the captured image is a feature value obtained from the brightness distribution of the entire captured image. This feature value Contrast Can be obtained simply by using a ratio between the maximum value of brightness and a predetermined value (minimum value or average value).
[0013]
The step of amplifying the image signal determines the amplification factor of the image signal based on the brightness level of the image signal obtained from the image sensor, and the contrast value of the captured image is predetermined. When the ratio exceeds the above-described contrast, the suppression rate for suppressing the amplification rate is further determined based on the contrast, and the image signal is amplified by the amplification rate to which the determined suppression rate is added.
[0014]
If the amplification factor is obtained from the brightness level of the captured image, an average amplification factor is determined regardless of the subject, the environmental light source, and the surrounding environment. In this case, when the degree of brightness is small and the contrast is large, for example, when only a person is photographed with flash in the dark, the amplification factor is applied to the image area of the subject that is the area of high brightness included in the captured image. Tend to increase. Therefore, if the suppression rate that suppresses the amplification factor is determined based on the contrast, and the image signal is amplified by the amplification factor added with the determined suppression factor, that is, the suppression factor increases as the amplification factor increases, An amplification factor suitable for the captured image can be determined, and an image with appropriate brightness can be obtained.
[0015]
At least one of an upper limit value and a lower limit value is set in the determined suppression rate.
[0016]
Set an upper limit value or a lower limit value for the determined suppression rate so that the captured image is not corrected in the direction of unnecessarily darkening or the captured image is not corrected in the direction of unnecessarily brightening. It is preferable. In particular, it is preferable to set the upper limit value to 1.
[0017]
The degree of brightness is an average value of brightness of the captured image or a weighted average value of brightness based on a predetermined position of the captured image.
[0018]
It is possible to evaluate the suitability of the light quantity of the captured image from the image signal acquired at the time of flash photography. In other words, if the amount of strobe light is inappropriate for the shooting scene, such as when the strobe light is not sufficiently irradiated, the amount of light is insufficient. A weighted average value of brightness based on the position of the captured image can be used. Thereby, the brightness such as the amount of light at the time of flash photography can be specified with high accuracy, and an image with appropriate brightness can be obtained.
[0019]
When determining the brightness level of the captured image, the captured image is divided into a plurality of blocks, the brightness level is determined for each block, and the brightness level is determined based on each of the determined brightness levels. It is characterized by calculating | requiring.
[0020]
In order to obtain the degree of brightness, it is possible to obtain a more accurate value by obtaining the brightness for each pixel and finally obtaining the degree of brightness of the captured image, but the processing becomes complicated. Therefore, as a method for determining the brightness level of the captured image, the shooting screen is divided into a plurality of blocks, and a brightness level for each block, for example, a numerical value indicating the brightness for each block is determined, It is preferable to obtain the brightness level based on each.
[0021]
For example, a weight coefficient corresponding to the position in the screen is set for a plurality of blocks, and the feature value of the brightness level is an integrated value obtained by integrating image signals for each block. The brightness level can be obtained by adding the integrated value for each block and the multiplication value of the corresponding weighting factor for all the blocks and dividing the total added value by the sum of the weighting factors. The amplification factor can be determined so that the main subject has an appropriate brightness based on the distribution of weighting factors in the shooting screen.
[0022]
The determined amplification factor is set to at least one of an upper limit value and a lower limit value. In particular, the lower limit value can be set to 1.
[0023]
If the amplification factor of the image signal is too large, the S / N ratio of the image deteriorates. Therefore, it is preferable to set an upper limit value for the determined amplification factor in order to perform appropriate amplification. There is also an aspect in which a lower limit value is set for the determined amplification factor so that the captured image is not corrected in an unnecessarily dark direction. In particular, when the correction in the direction of darkening the image is prohibited, the lower limit value is set to 1.
[0024]
The image processing method can be easily realized by the following image processing apparatus. Specifically, the image processing apparatus is based on an image signal obtained by the image sensor at the time of shooting accompanied by light emission of the strobe light emitting device. As a feature value of brightness including the maximum value of brightness obtained from the brightness of the entire captured image and a predetermined value set in advance Brightness calculation means for determining the brightness level of the captured image, contrast calculation means for determining the contrast of the captured image from the brightness level of the captured image, and the brightness level determined for the captured image On the basis of the Determine the amplification factor of the image signal When the contrast of the captured image exceeds a predetermined contrast value, a suppression rate for suppressing the amplification factor of the captured image is determined based on the contrast of the captured image. A decision means to Of the captured image to which the determined suppression rate is added. And amplifying means for amplifying the image signal according to an amplification factor.
[0025]
In addition, the image processing method can provide a more effective image by mounting the function on an electronic camera such as a digital camera. Specifically, the electronic camera includes an image sensor, a strobe control unit that controls the strobe light emitting device so as to give auxiliary light to the subject at the time of shooting, a storage unit that stores an image signal acquired through the image sensor, Amplifying means for amplifying the image signal stored in the storage means; As a feature value of brightness including the maximum brightness value obtained from the brightness of the entire captured image and a predetermined value set in advance Obtain the brightness level of the captured image, determine the contrast of the captured image from the brightness level of the captured image, and determine the brightness level of the captured image On the basis of the Determining the amplification factor of the image signal; When the contrast of the captured image exceeds a predetermined contrast value, Based on contrast The suppression rate for suppressing the amplification rate of the captured image is determined, and the captured image to which the determined suppression rate is added is determined. A control unit that performs variable gain control of the amplification unit according to the amplification rate, and a recording unit that records an image obtained as a result of amplification by the amplification unit on a recording medium are provided.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. In this embodiment, the present invention is applied to a digital camera.
[0027]
FIG. 1 shows a block diagram of a digital camera according to an embodiment of the present invention. The photographing optical system 12 of the camera 10 includes a photographing lens 14 and a diaphragm 16. The photographic lens 14 is composed of one or a plurality of lenses, and may be a single focal length (fixed focal length) lens or a variable focal length such as a zoom lens or a telephoto / wide-angle bifocal switching lens. Good.
[0028]
The subject image formed on the light receiving surface of the CCD 18 via the photographing optical system 12 is converted into signal charges of an amount corresponding to the amount of incident light by each sensor. The signal charge accumulated in this way is read out by a CCD drive pulse applied from the CCD drive circuit 20, and is sequentially output from the CCD 18 as a voltage signal (analog image signal) corresponding to the signal charge.
[0029]
The CCD 18 is provided with a shutter drain via a shutter gate, and the accumulated signal charge can be swept out to the shutter drain by driving the shutter gate with a shutter gate pulse. That is, the CCD 18 has a so-called electronic shutter function that controls the accumulation time (shutter speed) of charges accumulated in each sensor by the shutter gate pulse.
[0030]
The signal read from the CCD 18 is subjected to correlated double sampling (CDS) processing in the CDS circuit 22 and color separation processing into R, G, B color signals to adjust the signal level of each color signal (pre-white balance). Process).
[0031]
The image signal that has undergone the predetermined analog signal processing is applied to the A / D converter 24, converted into R, G, B digital signals by the A / D converter 24, and then stored in the memory 26. .
[0032]
A timing signal generation circuit (TG) 28 provides appropriate timing signals to the CCD drive circuit 20, the CDS circuit 22 and the A / D converter 24 in response to a command from the CPU 30, and each circuit generates a timing signal. It is driven in synchronism with a timing signal applied from the circuit 28.
[0033]
The CPU 30 is a control unit (control means) that comprehensively controls each circuit of the camera 10, and a gain adjustment circuit 34, a gamma correction circuit 36, and a luminance / color difference signal processing circuit (referred to as a YC processing circuit) 38 via a bus 32. The compression / expansion circuit 40, the card interface 44 of the memory card 42, the display driver 48 that drives the display unit 46, and the like are connected.
[0034]
The CPU 30 controls the corresponding circuit block based on the input signal from the operation unit 50, and controls the zooming operation, the automatic focus adjustment (AF) operation of the photographing lens 14, the automatic exposure adjustment (AE), and the like. .
[0035]
The operation unit 50 includes a release button that gives an instruction to start image recording, a camera mode selection unit, a zoom operation unit, and other various input units. These input means have various forms such as switch buttons, dials, and slide-type knobs. There is also an aspect in which a setting menu or a selection item is displayed on the screen of the touch panel or the liquid crystal monitor display unit, and a desired item is selected with a cursor. . The operation unit 50 may be disposed in the camera body, or may be configured as a remote control transmitter separated from the camera body.
[0036]
In the present embodiment, one of the input means of the operation unit 50 further includes a focus position setting button 51. The focus position setting button 51 is used to indicate the position of the main subject in the screen when the camera 10 captures the subject.
[0037]
That is, normally, it is set to focus on the subject at the center of the screen, assuming that the main subject is located at the center of the screen. However, there is a case where the main subject is positioned at a position deviated from the center of the screen in the composition (scene) assumed by the user. In this case, the focal point does not coincide with the main subject, but the focal point coincides with the central subject. Therefore, in the present embodiment, the focus position can be set in a shooting scene in which the main subject is located at a position off the center of the screen.
[0038]
FIG. 4 shows a conceptual configuration of the focus position setting button 51. The focus position setting button 51 includes an instruction button 51U for instructing to move the focus position from the initial position to the upper part, an instruction button 51D for instructing to move the focus position from the initial position to the lower part, and the focus position from the initial position to the left part. An instruction button 51L for instructing movement, an instruction button 51R for instructing movement of the focus position from the initial position to the right part, and an instruction button 51E for instructing selection of the focus area are configured. The focus position setting button 51 may display a setting menu or a selection item on the screen of the touch panel or the liquid crystal monitor display unit and select a desired item with a cursor.
[0039]
FIG. 5 shows a focus position with respect to a screen (for example, an image in the finder) 60 as a captured image. In this example, the focus area 62 indicates the position of the initially set screen center, and the focus area 62a is determined from the position of the focus area 62 that is initially set by the instruction button 51R and the instruction button 51D. , The focus position is changed to the position of the instruction focus area 62a. Further, the size of the focus area 62 can be instructed to select from the size of one or more predetermined focus areas by pressing the instruction button 51E. Thereby, the size of the focus area can be changed according to the size of the main subject.
[0040]
The CPU 30 in FIG. 1 performs various calculations such as a focus evaluation calculation and an AE calculation based on the image signal output from the CCD 18, and based on these calculations, driving means (for example, an AF motor, The iris lens 52 is controlled to move the focus lens to the in-focus position, and the aperture 16 is set to an appropriate aperture value.
[0041]
For example, a contrast AF method in which the focus lens is moved so that the high frequency component of the G signal is maximized is employed for the AF control. In the AE control, the subject brightness (shooting EV) is obtained based on the integrated value obtained by integrating the R, G, and B signals of one frame, the aperture value and the shutter speed are determined based on the taken EV, and the driving unit 52 is operated. In addition, the diaphragm 16 is driven, and the charge accumulation time of the CCD 18 is controlled by the electronic shutter so that the determined shutter speed is obtained. Therefore, only by directing the photographing lens 14 of the camera 10 toward the subject, optimal exposure adjustment is performed and focusing is automatically performed.
[0042]
At the time of shooting recording, when the release button is “half-pressed”, the above-mentioned photometric operation is repeated a plurality of times to obtain an accurate shooting EV, and the aperture value and shutter speed at the time of shooting are finally determined based on this shooting EV. . Then, when the release button is “fully pressed”, the aperture 16 is driven so that the final determined aperture value is obtained, and the charge accumulation time is controlled by the electronic shutter so that the determined shutter speed is obtained. In addition to the method of controlling AE and AF based on the image signal acquired from the CCD 18, a well-known photometric sensor, a distance measuring sensor including an AF light projecting / receiving sensor, or the like may be used.
[0043]
Further, the camera 10 has a strobe light emitting device 54 and a light receiving element 56 for dimming, and automatically controls the strobe light emitting device 54 at low brightness in response to an operation of a strobe mode setting button included in the operation unit 50. The “low-brightness automatic light-emission mode” in which light is emitted, the “forced light-emission mode” in which the strobe light-emitting device 54 emits light regardless of the subject brightness, or the “light-emission prohibition mode” in which light emission of the strobe light-emitting device 54 is prohibited.
[0044]
The CPU 30 controls charging of the main capacitor of the strobe light emitting device 54 and discharge (light emission) timing to the light emitting tube (for example, xenon tube) according to the strobe mode selected by the user, and performs measurement from the light receiving element 56. Based on the result, the emission stop is controlled. The light receiving element 56 receives the reflected light from the subject illuminated by the light emission of the strobe and converts it into an electrical signal corresponding to the amount of light received. The signal of the light receiving element 56 is integrated by an integration circuit (not shown), and the light emission of the strobe is stopped when the integrated light receiving amount reaches a predetermined appropriate light receiving amount.
[0045]
Data output from the A / D converter 24 is stored in the memory 26 and added to the integrating circuit 60. The integration circuit 60 divides the photographing screen into a plurality of blocks (for example, 64 blocks of 8 × 8), and performs integration calculation of the received G signal for each block. Note that the luminance signal (Y signal) may be generated from the R, G, and B data, and the luminance signal may be integrated. Further, the integrating circuit 60 can also be used as an AE arithmetic circuit. Information on the integrated value (calculation result) obtained by the integrating circuit 60 is input to the CPU 30.
[0046]
Based on the information received from the integration circuit 60, the CPU 30 calculates an evaluation value E of the photographic screen according to an algorithm described later, and determines a gain value (amplification factor) in the gain adjustment circuit 34 using the obtained evaluation value E. The CPU 30 controls the gain amount in the gain adjustment circuit 34 according to the determined gain value.
[0047]
The R, G, B image data stored in the memory 26 is sent to the gain adjustment circuit 34, where it is amplified. The amplified image data is subjected to a gamma correction process in a gamma correction circuit 36 and then sent to a YC processing circuit 38. The RGB data is converted into a luminance signal (Y signal) and a color difference signal (Cr, Cb signal). Converted.
[0048]
The luminance / color difference signal (abbreviated as YC signal) generated in the YC processing circuit 38 is written back to the memory 26. The YC signal stored in the memory 26 is supplied to the display driver 48, converted into a predetermined signal (for example, an NTSC color composite video signal), and output to the display unit 46. As the display unit 46, a liquid crystal display or other display device capable of color display is used. The display unit 46 may be a YC signal input type or an RGB signal input type, and a driver corresponding to the display device is applied.
[0049]
The image data is periodically rewritten by the image signal output from the CCD 18, and a video signal generated from the image data is supplied to the display unit 46, whereby the image captured by the CCD 18 is a moving image (live image) in real time. Or not in real time, but displayed on the display unit 46 as a substantially continuous image.
[0050]
The display unit 46 can be used as an electronic viewfinder, and the photographer can check the shooting angle of view by using a display image on the display unit 46 or an optical viewfinder (not shown). In response to a predetermined recording instruction (shooting start instruction) operation such as a release button pressing operation, capturing of image data for recording is started.
[0051]
When the photographer inputs a shooting / recording instruction from the operation unit 50, the CPU 30 sends a command to the compression / decompression circuit 40 as necessary, whereby the compression / decompression circuit 40 converts the YC data on the memory 26 into JPEG or another predetermined format. Compress according to The compressed image data is recorded on the memory card 42 via the card interface 44.
[0052]
When the mode for recording non-compressed image data (non-compression mode) is selected, the image data is recorded on the memory card 42 without being compressed without performing the compression processing by the compression / decompression circuit 40. The
[0053]
In the camera 10 of the present embodiment, a memory card 42 is used as means for storing image data. Specifically, a recording medium such as smart media is applied. The form of the recording medium is not limited to the above, and various forms such as a PC card, a micro drive, a multimedia card (MMC), a magnetic disk, an optical disk, a magneto-optical disk, and a memory stick are possible. Corresponding signal processing means and interfaces are applied.
[0054]
In the reproduction mode, the image data read from the memory card 42 is decompressed by the compression / decompression circuit 40 and output to the display unit 46 via the driver 48.
[0055]
The memory 26 and the memory card 42 according to the present embodiment correspond to the storage means of the present invention, and the CPU 30 includes the functions of the strobe control means and the control means of the present invention. The gain adjusting circuit 34 corresponds to the amplifying means of the present invention, and the image data recording process to the memory card 42 corresponds to the function of the recording means of the present invention.
[0056]
Next, image correction in the digital camera of this embodiment will be described.
[0057]
As shown in FIG. 2, the shooting screen is divided into 8 × 8 blocks in the integration circuit 60. Then, an integrated value Si of the G (green) signal in the image signal is calculated for each block Bi (i = 0, 1, 2,..., 63). As shown in FIG. 3, each block has a weight coefficient Wi (i = 0, 1, 2,..., 63). The weight coefficient Wi is set to a relatively large value at the center of the screen, and is set to a smaller value as the distance from the center increases.
[0058]
Since the main subject is often placed near the center of the screen, setting the distribution of weighting factors as shown in FIG. 3 makes it possible to perform an evaluation that sufficiently reflects the state of the subject at the center of the screen. It becomes possible. Note that the present invention is not limited to the arrangement of the weighting factors shown in FIG. 3, and the arrangement of the weighting factors determined in accordance with a predetermined screen distribution as to how the main subject is handled can be adopted.
[0059]
In addition, when the focus position is changed by a user instruction (instruction of the focus position by the focus position setting button 51 shown in FIG. 4), the distribution of the weighting coefficients shown in FIG. 3 corresponds to the changed focus position. Move and place. Thereby, the main subject reflecting the user's instruction can be grasped.
[0060]
Next, image correction for a captured image will be described. FIG. 6 is a flowchart showing the flow of image correction according to this embodiment. An image correction routine shown in FIG. 6 is executed in which a captured image is captured by flash photography. First, in step 100, an integrated value of brightness of the captured image is calculated. That is, the CPU 30 calculates the integrated value Si of the G (green) signal in the image signal included in each block Bi (i = 0, 1 to 63) based on the information from the integrating circuit 60. When the calculation of the integrated value Si for each block is completed, the process proceeds to the next step 102, and the evaluation value E is calculated according to the following equation (1) using the weight coefficient Wi (see FIG. 3).
[0061]
[Expression 1]

[0062]
That is, the evaluation value E is obtained by adding the multiplication value Si of each block Bi and the weighted coefficient Wi (Si × Wi) for all the blocks i = 0 to 63, and adding the total added value to the weighting coefficient Wi. It is obtained by dividing by (calculating a weighted average).
[0063]
In the next step 104, the average value and the maximum value of the brightness of the captured image are calculated. This is element data calculation processing for obtaining the contrast tendency of the captured image, and the contrast tendency value (hereinafter referred to as the contrast value Ct) corresponds to the variation rate with respect to the brightness of the captured image. In the present embodiment, the ratio between the maximum brightness value included in the captured image and the average brightness value of the captured image shown in the following equation (2) is adopted as the contrast value.
Ct = Cave / Cmax (2)
However, Cmax represents the maximum brightness value included in the captured image, and Cave represents the average brightness value of the captured image.
[0064]
Note that instead of the average value of brightness, a minimum value of brightness or a specified value representing an average level or low level brightness obtained by a predetermined function may be used. In the present embodiment, the contrast value Ct is calculated using the integrated value Si of the G (green) signal in the image signal for the block i = 0 to 63. In this case, since the main image (image of the main subject) is often distributed near the center of the captured image, the maximum value and the average value of the brightness can be obtained for the block at the center of the captured image. preferable.
[0065]
When the focus position is changed according to a user instruction (instruction for focus position by the focus position setting button 51 shown in FIG. 4), the changed focus area is set as the main image area. The maximum value and average value of brightness are obtained for the blocks. Thereby, it is possible to grasp the contrast of the main subject reflecting the user's instruction.
[0066]
In the next step 106, it is determined whether or not the evaluation value E, which is the calculation result of the formula (1), is less than “1”. If the evaluation value E is less than “1” and the determination is affirmative, the process proceeds to step 108. The evaluation value E is replaced with “1”, and the process proceeds to step 110. That is, when the evaluation value E is smaller than 1, it is clipped to E = 1. On the other hand, when a negative determination is made at step 106, that is, when the evaluation value E is "1" or more and a negative determination is made, the routine directly proceeds to step 110.
[0067]
In step 110, using the evaluation value E calculated as described above, a gain G representing the amplification degree of the image signal is calculated according to the following equation (3).
G = L / E (3)
However, L is a value indicating a predetermined target level.
[0068]
Next, the calculated gain G is accommodated (clipped) at a value between a predetermined upper limit value (GU, eg, 2.0) and a lower limit value (GL, eg, 1.0). First, in step 112, it is determined whether or not the calculated gain G is less than the lower limit value GL. If the gain G is less than the lower limit value GL and an affirmative determination is made, the process proceeds to step 114 and the gain G is set to the lower limit value GL. Replace and go to Step 120. That is, when the gain G is smaller than the lower limit value GL, clipping is performed to G = GL.
[0069]
On the other hand, if the determination in step 112 is negative, that is, if the gain G is greater than or equal to the lower limit GL, the process proceeds to step 116. In step 116, it is determined whether or not the gain G exceeds the upper limit value GU. If the gain G exceeds the upper limit value GU and an affirmative determination is made, the process proceeds to step 118, the gain G is replaced with the upper limit value GU, and the process proceeds to step 120. move on. That is, when the gain G is larger than the upper limit value GU, clipping is performed to G = GU.
[0070]
The reason for clipping to the upper limit value is that the amplification is limited to an appropriate gain amount because the S / N of the image deteriorates if the gain amount is too large. Although the specific setting of the upper limit value GU is various, for example, when the image signal is represented by 8 bits, the upper limit of the amplification factor is set to 3 times. Further, when it is not desired to correct the image in the darkening direction, the lower limit value GL may be set to 1.
[0071]
In step 120, a suppression gain CG is calculated. The suppression gain CG appropriately corrects the brightness of the subject even in a shooting scene with a dark background, for example, by suppressing the gain G that is uniquely corrected by the brightness when the contrast of the captured image is large. Is for.
[0072]
As shown in FIG. 7, in the present embodiment, the suppression gain CG is determined by the contrast value Ct. That is, a characteristic CC representing the relationship between the suppression gain CG and the contrast value Ct is determined in advance, and the suppression gain CG corresponding to the contrast value Ct obtained in step 104 is calculated. The characteristic CC is a characteristic in which the suppression gain CG maintains the upper limit value 1.0 until a predetermined contrast value Cta, and the suppression gain CG gradually decreases to the maximum value Ctb of the contrast value Ct. That is, as the calculation result of the above equation (2) increases, the suppression gain CG decreases. This corresponds to the suppression gain CG decreasing as the contrast of the captured image decreases, or increasing as the contrast of the captured image increases.
[0073]
Note that the upper limit value is set for the suppression gain because it is assumed that the original gain amount for the image cannot be secured if the suppression amount is too large, and the suppression is limited to an appropriate gain amount.
[0074]
The contrast value Cta is a boundary contrast value Ct at which the strobe light is assumed not to reach the subject, and it is determined that there is little influence on the subject image even when the gain G calculated in step 110 is corrected. The average value or statistical value obtained by experiment or the like. In the present embodiment, a case will be described in which a characteristic CC that maintains a suppression gain CG of 1.0 until the contrast value Cta is used, but the present invention is not limited to this. For example, it is possible to employ a characteristic CCa in which the suppression gain CG gradually decreases as the contrast value Ct increases.
[0075]
In the next step 122, the correction gain Gall when the image is finally corrected is calculated using the gain G calculated in step 110 and the suppression gain CG calculated in step 120 and the following equation (4). To do.
Gall = (G−1.0) · CG + 1.0 (4)
The correction gain Gall calculated in step 122 is to obtain a correction value in which the gain G is suppressed by the magnitude of the contrast value Ct. That is, when the contrast is high, it is assumed that a strobe light has arrived and a captured image of moderate brightness is obtained on the subject, and the gain G obtained from the brightness is suppressed to reduce the image correction amount for the main subject image. Find the gain.
[0076]
The mathematical formula for calculating the correction gain Gall is not limited to the above formula (4). For example, a strobe light arrives and a captured image with moderate brightness is obtained on the subject, but the gain G obtained from the brightness is suppressed for the image, and the image correction amount for the image of the main subject is reduced. What is necessary is just to obtain | require a gain, and what is necessary is just to comprise using a polynomial and arbitrary functions.
[0077]
In the next step 124, the gain adjustment circuit 34 amplifies the image signal in accordance with the correction gain Gall determined in step 122, corrects the captured image, and ends this routine.
[0078]
Note that the processing of step 100 and step 102 of the present embodiment corresponds to the function of the brightness calculation means of the present invention, and the processing of step 104 corresponds to the function of the contrast calculation means of the present invention. The processing from step 106 to step 122 corresponds to the function of the determining means of the present invention, and the processing of step 124 corresponds to the feeling of the amplifying means.
[0079]
As described above, according to the camera 10 of the present embodiment, when the photographed image is insufficient in light quantity based on the evaluation value E, the image signal is amplified by the gain adjustment circuit 34 according to the degree of the lack. Therefore, the shortage of the light emission amount of the strobe light emitting device and the lack of control accuracy of the light emission amount are compensated, and the main subject is displayed with an image having an appropriate brightness (for example, the face of the person who is the main subject when displayed on the display unit 46). A bright image that can be seen).
[0080]
In this embodiment, the contrast of the captured image is calculated, and the gain of the image signal to be amplified by the gain adjustment circuit 34 is determined according to the contrast. That is, it is determined whether or not strobe light has reached the main subject based on the contrast, and the gain G determined by the brightness of the captured image is suppressed from the determination result value (contrast value). As a result, when the contrast is high, the strobe light arrives and a captured image of moderate brightness is obtained on the subject, and the gain G obtained from the brightness is suppressed, and the image correction amount for the image of the main subject is reduced. Even when the image is taken in an environment where the surroundings are dark, the image of a person with a proper brightness of the main subject (for example, seeing the face of a person such as the main subject when displayed on the display unit 46) Can be obtained).
[0081]
【The invention's effect】
As described above, according to the present invention, by determining the amplification factor based on the brightness level and contrast of the captured image, an amplification factor suitable for the captured image of the subject at the time of flash photography can be determined. There is an effect that an image having appropriate brightness can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram of a digital camera according to an embodiment of the present invention.
FIG. 2 is an image diagram showing an example of a division form of a photographing screen in an integration circuit used for image correction.
FIG. 3 is an image diagram showing an example of a weighting factor Wi assigned to each block of a shooting screen.
FIG. 4 is an image diagram showing a schematic configuration of a focus position setting button.
FIG. 5 is an image diagram showing a process in which a focus area is changed by an instruction of a focus position setting button.
FIG. 6 is a flowchart showing a flow of image correction processing in the camera according to the embodiment.
FIG. 7 is a characteristic diagram showing the relationship between contrast and suppression gain.
[Explanation of symbols]
10 ... Camera
12 ... Photography optical system
18 ... CCD
26 ... Memory
30 ... CPU
34 ... Gain adjustment circuit
42 ... Memory card
44 ... Card interface
50. Operation unit
51 ... Focus position setting button
54. Strobe light emitting device
62 ... Focus area at the center of the screen
Ct: Contrast value
CC ... Characteristics
CG ... Inhibition gain
Gall: Correction gain
G ... Gain

Claims (3)

Imaging as a brightness feature value including a maximum brightness value determined from the brightness of the entire captured image and a predetermined value based on an image signal obtained from the imaging device during shooting with light emission of the strobe light emitting device Determining the brightness of the image;
Obtaining a contrast of the captured image from the brightness level of the captured image;
Based on the degree of calculated brightness of the captured image to determine the amplification factor of the image signal, in the case where the contrast of the captured image exceeds a predetermined contrast value, the imaging based on the contrast of the captured image Determining a suppression rate for suppressing the amplification factor of the image, and amplifying the image signal by the amplification factor of the captured image to which the determined suppression rate is added ;
An image processing method comprising: Imaging as a brightness characteristic value including a maximum brightness value determined in advance from the brightness of the entire captured image and a predetermined value based on an image signal obtained by the imaging device during shooting with light emission of the strobe light emitting device Brightness calculation means for determining the brightness level of the image;
Contrast calculation means for obtaining the contrast of the captured image from the brightness level of the captured image;
The amplification factor of the image signal is determined based on the degree of brightness obtained for the captured image, and the imaging based on the contrast of the captured image when the contrast of the captured image exceeds a predetermined contrast value Determining means for determining a suppression rate for suppressing the amplification factor of the image ;
Amplifying means for amplifying the image signal by the amplification factor of the captured image to which the determined suppression rate is added ;
An image processing apparatus comprising: An image sensor;
Strobe control means for controlling the strobe light emitting device so as to give auxiliary light to the subject at the time of shooting;
Storage means for storing an image signal acquired via the image sensor;
Amplifying means for amplifying the image signal stored in the storage means;
The degree of brightness of the captured image as a brightness characteristic value including a maximum brightness value determined from the brightness of the entire captured image and a predetermined value set in advance is obtained, and the captured image is determined from the brightness level of the captured image. The image signal amplification factor is determined based on the obtained brightness level of the captured image. When the contrast of the captured image exceeds a predetermined contrast value, the contrast of the captured image is determined. A control unit for determining a suppression rate for suppressing the amplification rate of the captured image based on the control unit, and performing amplification factor variable control of the amplification unit according to the amplification rate of the captured image to which the determined suppression rate is added ;
Recording means for recording an image obtained as a result of amplification by the amplification means on a recording medium;
An electronic camera characterized by comprising:

Images